Power plants that burn solid fuel have large amounts of ash that must be removed from the boiler and disposed of in a manner that is environmentally acceptable. Heavy solid particles of ash are usually dumped under or forward of the fire bed and accumulate in pit from which the ash is removed periodically or continually by mechanical means. Very light ash particles are crried by the flue gases that eventually rise through a stack for discharge to the atmosphere. These particles are usually removed from the flue gases by a dry dust collector followed by wet scrubbing or by an electrostatic precipitator. In between the heavy solids and the very light solids are the intermediate solids which are heavy enough to settle out from quiescent gases, but light enough to be carried along by a moving gas stream. Such particles may be as large as can be carried by the moving gas stream, although they usually are not larger than about 0.10 inch in diameter. Normally the intermediate solids are dumped into a hopper and removed from the hopper by a rotary seal valve which removes the ash without disturbing the vacuum in the boiler. This procedure has been unsatisfactory because there is no visible means for seeing whether the system is working, and in any event the wear and tear on rotary feeders is so great that there is too much maintenance for an economical operation.
It is an object of this invention to provide an improved method and apparatus for removing ash from the flue gases leaving the boiler. It is another object of this invention to provide a more economical means for removing ash from boilers. Other objects will appear from the more detailed description of this invention which follows.